A great deal of developmental activity has been expended to eliminate the costly, labor intensive cut and sew method of wrapping fabric about a cellular foam pad in automotive seat fabrications. One such development employs contact adhesives applied to the fabric layer and the foam pad to adhesively bond them together. However, once the adhesive is applied, it is difficult to properly position the fabric onto the foam pad resulting in misalignment and/or wrinkles in the bonded fabric.
Other developments include placing a heat-sensitive adhesive fabric or film between the fabric and the foam pad and subsequently melting the adhesive to effectuate bonding. One known technique for melting the adhesive employs a heated pressing mold in contact with the fabric layer to conduct heat through the fabric layer which, in turn, melts the adhesive. In addition to being time consuming, this technique causes nonuniform bonding due to an uneven temperature distribution throughout the adhesive. Additionally, many fabric types which are otherwise well suited for seating applications are made from materials which cannot withstand the high temperature ranges encountered with this technique, thus rendering unusable these otherwise desirable materials.
Another technique for heating and melting the adhesive film uses heated steam injected through either the fabric layer or the foam pad to melt the adhesive. Such a technique is disclosed in U.S. Pat. No. 4,692,199 to Kozlowski et al, assigned to the assignee of the present invention. The mold surfaces may also be heated in addition to the injection of steam to assist in the melting of the adhesive as is disclosed in U.S. Pat. No. 4,737,226 to Inoue. As discussed above, certain seat cover fabrics are sensitive to high temperature environments and thus may be damaged by the injection of heated steam. Another disadvantage of the steam injection method is that an amount of steam in excess of that necessary to melt the adhesive is required due to condensation and temperature loss as the steam passes through the fabric layer or the foam cushion prior to reaching the adhesive. Consequently, once the bonding process is completed, the excess steam must be extracted from the cushion assembly to prevent moisture damage to the assembly.
Industrial applications of microwave radiation heating have thus far been limited to the heating of rubber as disclosed in U.S. Pat. No. 4,104,098 to Hush et al, and for preheating plastics prior to a forming operation as disclosed in U.S. Pat. No. 4,579,617 to Oberg et al and in an article appearing in the March 1987 issue of High Technology, entitled "Industry Warms Up to Microwave Ovens," by Zygmont.